Continuous Wave High Frequency Ignition System

Abstract

An ignition system employing a unitary magnetic circuit type of oscillator to supply continuous wave high frequency spark signals controlled by the breaker points. It has a control winding and auxiliary elements to ensure positive starting and stopping of the oscillator as required for sparking intervals.

Description

CROSS REFERENCES TO RELATED APPLICATIONS

The following co-pending applications are referred to in this application as containing related subject matter:

Ser. No. 38,279 filed May 18, 1970, for "Saturable Core Square Wave Oscillator Circuit":, and

Ser. No. 87,549 filed Nov. 6, 1970, for "High Frequency Type Ignition System"

BOTH BEING FILED IN THE NAME OF THE APPLICANT OF THIS INVENTION, I.E., Robert E. Canup.

BACKGROUND OF THE INVENTION

1. Description of the Prior Art

While various proposals have been suggested for supplying continuous wave high frequency sparking energy, in an ignition system, the proposed arrangements have not operated satisfactorily for various reasons. Among the difficulties are those encountered in controlling the oscillator that generates the sparking energy. One type of oscillator employed is that known as a Uchrin-Royer type which employs a single saturable core transformer. It conventionally has the oscillation frequency determined by the number of winding turns employed and cross section area of the core. However, there have been substantial difficulties in the ability to apply this type oscillator to an ignition system.

Consequently, it is an object of the invention to provide an improved high frequency continuous wave ignition system that employs a unitary magnetic circuit type of oscillator.

SUMMARY OF THE INVENTION

Briefly, the invention is applicable to a continuous wave high frequency igniton system having breaker points and a unitary magnetic circuit type of oscillator. It concerns the improvement which comprises starting means for said oscillator. Such starting means comprises means associated with said breaker points for applying a magnetic bias to said magnetic circuit when said breaker points are in one position, and removing said bias when said breaker points go to the other position. It also comprises means for absorbing the initial surge effects at said breaker points when said bias is removed, whereby said oscillator circuit will start and continue oscillating while said breaker points are in said other position.

Again, briefly, the invention relates to a continuous wave high frequency ignition system which includes breaker points and which employs a single core transformer with a pair of transistors connected in an oscillator circuit. The oscillator circuit has a battery for its DC supply and the invention concerns the improvemement which comprises a control winding on said transformer. It also comprises circuit means including said breaker points in series with said control winding and having a potenio-meter connected across said battery for supplying a small DC current in said control winding in order to apply a magnetic bias to said core when said breaker points are closed. In addition, it comprises a small capacitor connected across said breaker points to absorb preliminary surge when the points begin to open, and a diode bridge having two pairs of diagonals one for input AC current flow and one for rectified DC output. It also comprises circuit means for connecting said input diagonal pair across said breaker points, in parallel with said small capacitor. And it comprises a larger capacitor with a discharge resistor being connected thereacross, and circuit means for connecting said larger capacitor and resistor to said output diagonal pair.

Once more, briefly, the invention concerns a continuous wave high frequency igntiion system that has breaker points and that employs a unitary magnetic circuit type oscillator including a battery for DC supply and having an output winding to supply sparking potential, as well as having a control winding. The invention comprises the combination of (1) circuit means comprising a potentiometer connected across said battery and connecting said breaker points in series with said control winding for applying a DC magnetic bias to said oscillator core when the points are closed. Also, it comprises (2) low impedance current flow path for induced currents in said control winding when said points are closed, in order to stop said oscillator. It also comprises (3) a large capacitor and circuit means for connecting it close to the common connector for the primary windings of said oscillator, and (4) a small capacitor connected across said breaker points for absorbing initial surge potnetial as said points commence opening. It also comprises (5) a diode bridge having two pairs of diagonals, and (6) an intermediate capacitor having a resistor connected thereacross for discharging the same. In addition, it comprises (7) circuit means for connecting said diode bridge with one pair of said diagonals across said breaker points for AC current flow, and (8) circuit means for connecting said intermediate capacitor across said other pair of diagonals to receive rectified DC charging current for absorbing secondary surge potential as said points continue opening until the points are open far enough to prevent arcing.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and benefits of the invention will be more fully set forth below in connection with the best mode contemplated by the inventor of carrying out the invention, and in connection with which there are illustrations provided in the drawings, wherein:

FIG. 1 is a schematic circuit diagram illustrating a typical igniton system according to the invention; and

FIG. 2 is a schematic diagram showing a transformer core with windings thereon corresponding to the windings of FIG. 1 and including an air gap in the core.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, it is to be noted that the circuit diagram illustrated shows a unitary magnetic circuit type of oscillator 11 that basically resembles the type of oscillator known as a Uchrin-Royer circuit. Such an oscillator operates in a known manner (as will be described in greated detail below) to supply a continuous-wave high frequency signal in an output winding 12, that is located on a transformer 13. The power supply for the oscillator is a DC battery 16 that is connected to ground at one terminal by a circuit wire 17, as illustrated. The other side of the battery is connected via a wire 18, and an ignition switch 19 to a circuit wire 20. Wire 20 is connected to another circuit wire 24 that leads to a wire 25 which connects into the center tap on a primary winding 26 located on the transformer 13. In this manner the power necessary for driving the oscillator 11 is supplied to the emitters of a pair of transistors 30 and 31. These have the collectors thereof joined together in a common circuit and it is connected to a ground via a circuit wire 32.

As indicated above, the operation of oscillator 11 is well known. It consists of an alternate switching of a state of full conduction from one to the other of the transistors 30 and 31. This takes place by reason of the action involving a pair of base drive windings 35 and 36. These windings are connected from the emitter to the base of transistors 31 and 30 respectively, via the indicated circuit wires which include resistors 37 and 38.

The alternate switching action creates a square wave output from the winding 12 at a frequency which, in prior oscillators of this type would depend upon the number of turns in windings 26, 35 and 36 and upon the cross section area of the core of transformer 13. However, it is to be noted that in the system according to this invention, there is a structure such that the frequency of the oscillation depends instead more upon the load and current flow conditions through the transistors 30 and 31 than upon magnetic flux conditions in the core of the transformer 13. Therefore, the core area and the size of an air gap 42 (FIG. 2) will substantially effect but not be the sole determinant of the frequency.

Operation in the foregoing manner provides the advantages which have been more fully described in my co-pending application, Ser. No. 38, 279 filed May 18, 1970 titled "Saturable Core Square Wave Oscillator Circuit." A major benefit of this arrangement is that of controlling the frequency of oscillation in dependence upon the load on the output circuit. Therefore, with a negative resistance type load (which a sparking circuit represents), the output circuit including transformer 13 may be designed for resonance at no load. This will cause an extra high voltage at the beginning of oscillation, while it will be reduced as the load caused by the sparking discharge develops. Thus, unnecessary power dissipation both in the sparking circuit and in the oscillator circuit will be avoided.

The system according to this invention employs a control winding 45 that is magnetically coupled to the core of transformer 13 and that is connected to a potentiometer made up of resistors 46 and 47 which are connected in series across the output of the battery 16. It will be noted that one side of winding 45 is connected via a circuit wire 50 to the junction between the resistors 46 and 47. The other side of the winding 45 is connected via a circuit wire 51 to one side of a "breaker points" switch 52. The other side of switch 52 is connected to ground via a circuit wire 53, as illustrated.

When the breaker points switch 52 is closed, the potential drop across resistor 47 will be applied to the winding 45. This will cause DC current flow and the circuit constants are designed so as to cause a desired magnetic bias on the core of transformer 13. Such bias will act to insure immediate starting of the oscillator 11 upon opening of the breaker points 52. Thus, when the steady state magnetic flux caused by the foregoing small current flow in winding 45 collapses, it will induce signals in windings 26, 35 and 36 such that the oscillator 11 is driven into oscillation by the conventional action for this type of oscillator. The collasping field causes one transistor to draw base current while the other remains cut off and the windings are properly phased to cause the resulting collector current to aid the voltage induced by the flux decay so that the oscillation starts. Thereafter the reverse action takes place on the next half cycle.

It is to be noted, however, that the foregoing surge which tends to take place upon the collapse of the field from winding 45, will induce a signal to reinforce the collapsing field conditions as the oscillator starts its first surge toward oscillation. The voltage thus induced in winding 45 will rapidly rise to an amplitude which tends to cause arcing across the contacts of breaker points 52. While a conventional approach to overcoming such arcing conditions would be to connect a capacitor across the breaker points 52, it has been found that such a capacitor having enough capacity to absorb the surge energy and void the arcing conditions, will load down the oscillator system sufficiently to prevent oscillation. Therefore, this invention makes use of a small capacity capacitor 56 that is connected across the breaker points 52, but that has only quite limited electrical capacity. It is employed for absorbing the initial surge and reducing interference signals.

In addition there is provided a diode bridge 57 that is connected with one pair of its diagonals across the breaker points 52, in parallel with the capacitor 56. Thus, there is a circuit wire 60 connected to one diagonal point of the diode bridge 57 and to the circuit wire 51. And, there is another circuit wire 61 that connects the opposite diagonal point of the bridge 57 to ground, as illustrated.

It will be observed that the diodes in bridge 57 are connected with the polarities arranged so as to provide a rectified DC output at the diagonal points opposite the pair of diagonals that are connected to circuit wires 60 and 61. Thus, there is a circuit wire 64 connected to one of these opposite diagonal points and another circuit wire 65 connected to the other of this pair of diagonals. These circuit wires 64 and 65 connect to the ends of an intermediate sized capacitor 66 which has a resistor 67 connected thereacross in order to provide a discharge path for the capacitor. As will be indicated more fully hereafter, this intermediate capacitor 66 along with the diode bridge 57 act to absorb the surge voltage after the small capacitor 56 has been charged.

An additional feature of this invention concerns that of providing a large capacity capacitor 70 which is connected as close as feasible to the circuit wire where it connects to the center tap on the winding 26. Thus, capacitor 70 in the circuit diagram has one side connected to the junction between circuit wires 24 and 25 while the other side thereof is connected to ground, as illustrated. This has two functions, one of which is to limit switching spikes on the primary wave form in the transistor circuits. The other function is to reduce feedback to the battery 16. Such feedback would tend to cause interference with radio equipment operated from the same battery.

OPERATION

The operation of the ignition system has been indicated above as to specific aspects, but it may be made additionally clear with reference to FIG. 1, as follows:

Starting with conditions when the breaker points 52 are closed (and of course ignition switch 19 is closed), there is a small DC current flowing through the winding 45 as determined by the potential drop across resistor 47 of the potentiometer 46-47. This DC current in control winding 45 sets up a biasing steady state flux in the core of transformer 13, and this bias acts to insure that the magnetic conditions in the core will always be such as to cause starting of the oscillator immediately upon de-energization of the control winding 45. An explanation of this action, in greater detail, is provided in my co-pending application Ser. No. 87,549 filed Nov. 6, 1970 titled High frequency Type Ignition System (D-71,721).

When the breaker points 52 are closed, following a period of sparking oscillations, the oscillator will stop oscillating. This is because there is a low impedance path for current flow that is caused by voltages induced in the winding 45. The current which flows in this path will load down the oscillator to the point where oscillation ceases which, of course, stops the ignition spark output.

The low impedance path across the ends of the winding 45 may be traced from ground at one side of the closed breaker points switch 52, over the wire 51 to one side of the winding. Then from the other side of the winding 45 the path is over wire 50 and through resistor 47 back to ground.

It may be noted that if desired the resistor 47 might be replaced by a pair of diodes (not shown) to connect circuit wire 50 to ground. These would be oppositely poled so as to provide low impedance paths for both directions of flow of AC signal, as generated in the winding 45. However, the same result is accomplished by using resistor 47 even though it will dissipate more power, by drawing potentiometer current, than would be the case if the foregoing diodes (not shown) were employed.

An important aspect of the invention is that involving the starting network which was described above. It includes the diode bridge 57 and the small capacitor 56 which are both connected across the breaker points 52. In operation, the action of this starting network may be described by tracing conditions which are emphasized during a slow speed operation of an internal combustion engine to which this ignition system may be applied.

Thus, as breaker points 52 commence opening, the DC current flowing in winding 45 is cut off and the collapsing magnetic field thus created in the core of transformer 13 tends to cause the oscillator 11 to start. The action may be described as that of driving one transistor toward full conduction while cutting the other transistor off. Such transient conditions, or surge, will induce high voltages in the windings and particularly in winding 45. In other words, a voltage immediately builds across the opening breaker points 52, and this tends to ionize the gap as it opens which would cause an arc and thus permit substantial current flow to be induced.

However, since such current flow, if permitted, would load down the magnetic circuit and thus stop the oscillator at the inception; such conditions are avoided by the provision of small capacitor 56. This capacitor is charged by the initial surge potential and accompanying current flow until a predetermined voltage is reached, which in the illustrated system may be about 1.2 volts (in the case where silicon diodes are employed in the bridge 57). At that point, the surging potential would again tend to cause arcing at breaker points 52. But now, the bridge 57 will draw current flow through the properly poled pair of diodes that are conducting, and this will charge the intermediate sized capacitor 66.

It will be observed that the foregoing action may include surges in either direction of AC potentials since the bridge 57 is arranged for rectified DC output across the capacitor 66. In this manner then, the intermediate surging effects will be drained off by charging capacitor 66 during the time that the breaker points 52 are continuing to open and until they have opened sufficiently to prevent arcing thereacross. However, the loading down of the oscillator circuit is prevented after the initial starting of the oscillator when the capacitor 66 is charged. Then, upon opening of the breaker points 52 the oscillator will not be loaded and the oscillator will thereafter continue to run and provide sparking output signals from the winding 12, until the breaker points 52 have been closed once more.

An additional function of the starting network 57, 66 and 67, is that of absorbing oscillator switching transients in the control winding 45 circuit. Such switching transients occur as one transistor turns on and the other turns off, and this is the time when the capacitor 66 is being recharged to its peak voltage after the previous half cycle's discharge through resistor 67. Consequently the transient is absorbed by the recharging current flow. This helps to prevent these switching transients from reaching voltage magnitudes that would be sufficient to cause breakdown of the collector to emitter junction of the transistors.

A preferred set of circuit constants that has been found quite satisfactory for an ingition system according to that illustrated in FIG. 1, is as follows:

Transistors 30 and 31 -- type manufactured by

Solitron Devices Inc., Part. No. SDT-1809.

Resistors 37 and 38 -- 1.0 ohms each.

Capacitor 70 -- 1500 uf at 25 volts.

Resistor 46 -- 30 ohms.

Resistor 47 --12 ohms.

Resistor 67 -- 5600 ohms.

Capacitor 56 -- .01 uf at 2,000 volts.

Capacitor 66 -- 0.15 uf at 400 volts.

Diode bridge 57 -- bridge rectifier, manufactured by Mallory, FW-600 MAL 935.

Transformer 13 -- winding 26, 18 turns (9--9) winding 35, 4 turns winding 36, 4 turns winding 12, 9000 turns winding 45, 100 turns.

Battery 16 -- a 12-volt DC battery.

While a particular embodiment of the invention has been described above in considerable detail in accordance with the applicable statutes, this is not to be taken as in any way limiting the invention, but merely as being descriptive thereof.

Claims

I claim:

1. In combination with a continuous wave high frequency ignition system having breaker points, said system comprising an oscillator, said oscillator including a transformer for delivering spark energy and said oscillator employing a unitary magnetic circuit including the core of said transformer, the improvement comprising

starting means for said oscillator, comprising

1.

a. a control winding linking said unitary magnetic circuit,

b. circuit means including said breaker points for applying DC bias to said control winding when said breaker points are in one position and removing said bias when said breaker points go to the other position, and

2. means for absorbing the initial surge effect at said breaker points when said bias is removed whereby said oscillator circuit will start and continue oscillating while said breaker points are in said other position.

2. An ignition system according to claim 1 wherein said absorbing means (2) comprises

c. a small capacitor across said breaker points, and

d. diode means coupled to a larger capacitor connected across said breaker points.

3. An ignition system according to claim 2 wherein said diode means (d) comprises

d1. a diode bridge having two pairs of diagonal points, and

d2. circuit means for connecting one pair of diagonal points across said breaker points and for connecting the other pair of diagonal points across said larger capacitor.

4. An igniton system according to claim 2 wherein said absorbing means (2) further comprises

e. a resistor connected across said larger capacitor.

5. In a continuous wave high frequency ignition system including breaker points and employing a single core transformer having a pair of transistors connected in an oscillator circuit, said circuit having a battery for DC supply, the improvement comprising

a control winding on said transformer,

circuit means including said breaker points in series with said control winding and having a potentiometer connected across said battery for supplying a small DC current in said control winding in order to apply a magnetic bias to said core when said breaker points are closed,

a small capacitor connected across said breaker points to absorb preliminary surge when the points begin to open,

a diode bridge having two pairs of diagonals one for input AC current flow and one for rectified DC output,

circuit means for connecting said input diagonal pair across said breaker points in parallel with said small capacitor,

a larger capacitor and discharge resistor thereacross, and

circuit means for connecting said larger capacitor and resistor to said output diagonal pair.

6. A continuous wave high frequency ignition system having breaker points and a control winding and employing a unitary magnetic circuit type of oscillator, including primary windings and a secondary winding for delivering sparking output signals, comprising in combination

means for applying a DC potential to said control winding when said breaker points are in one position and for removing said DC potential when the breaker points are in the other position, and

means for applying a low impedance path across said control winding when said breaker points are in said one position in order to stop said oscillator.

7. A continuous wave high frequency ignition system according to claim 6, further comprising

capacitor means closely connected to the primary windings of said oscillator for absorbing switching peaks during oscillation.

8. A continuous wave high frequency ignition system according to claim 7, further comprising

means for absorbing initial surge potential at said breaker points when moving toward said other position without loading said control winding enough to prevent starting of said oscillator.

9. A continuous wave high frequency ignition system according to claim 6 wherein said system also has an output winding to supply sparking potential, further comprising

means for determining the frequency of said oscillator in dependence upon leakage inductance in said magnetic circuit whereby the load on said output winding may be controlled by a change in the frequency.

10. A continuous wave high frequency ignition system according to claim 9, further comprising

capacitor means closely connected to the primary windings of said oscillator for absorbing switching peaks during oscillation.

11. A continuous wave high frequency ignition system according to claim 10 further comprising

means for absorbing initial surge potential at said breaker points when moving toward said other position without loading said control winding enough to prevent starting of said oscillator.

12. A continuous wave high frequency ignition system according to claim 11, wherein said absorbing means comprises

a small capacitance capacitor connected across said breaker points, and

a diode-coupled larger capacitance capacitor connected across said breaker points in parallel with said small capacitor.

13. A continuous wave high frequency ingition system having breaker points and employing a unitary magnetic circuit type oscillator including a battery for DC supply and having an output winding to supply sparking potential, and a control winding, comprising in combination

1. circuit means comprising a potentiometer connected across said battery and connecting said breaker points in series with said control winding for applying a DC magnetic bias to said oscillator core when the points are closed,

2. low impedance means comprising a portion of said potentiometer and providing a low impedance current flow path for induced currents in said control winding when said points are closed in order to stop said oscillator,

3. a large capacity capacitor and circuit means for connecting it close to the common connector for the primary windings of said oscillator,

4. a small capacity capacitor connected across said breaker points for absorbing initial surge potential as said points commence opening,

5 a diode bridge having two pairs of diagonals,

6 an intermediate capacity capacitor having a resistor connected thereacross for discharging same,

7. circuit means for connecting said diode bridge with one pair of diagonals across said breaker points for AC current flow, and

8 circuit means for connecting said intermediate capacitor across said other pair of diagonals to receive rectified DC charging current for absorbing secondary surge potential as said points continue opening until the points are open far enough to prevent arcing.

14. In combination with a continuous wave high frequency ignition system having engine timed current flow control means, said system comprising an oscillator, said oscillator including a transformer for delivering spark energy and said oscillator employing a unitary magnetic circuit including the core of said transformer, the improvement comprising

starting means for said oscillator, comprising

1.

a. a control winding linking said unitary magnetic circuit,

b. circuit means including said current flow control means for applying DC to said control winding,

2. initial surge absorbing means comprising

c. a small capacitor across said current flow control means, and

d. diode means coupled to a larger capacitor connected across said current flow control means, said diode means comprising

d1. a diode bridge having two pairs of diagonal points, and

d2. circuit means for connecting one pair of diagonal points across said current flow control means and for connecting the other pair of diagonal points across said larger capacitor.

15. In a continuous wave high frequency ignition system including engine timed current flow control means and employing a single core transformer having a pair of transistors connected in an oscillator circuit, said circuit having a battery for DC supply, the improvement comprising

a control winding on said transformer,

circuit means including said current flow control means in series with said control winding and having a potentiometer connected across said battery for supplying a small DC current in said control winding in order to apply a magnetic bias to said core when said current flow control means is passing current,

a small capacitor connected across said current flow control means to absorb preliminary surge when the current flow control means begins to cut off current flow,

a diode bridge having two pairs of diagonals, one for input AC current flow and one for rectified DC output,

circuit means for connecting said input diagonal pair across siad current flow control means in parallel with said small capacitor,

a larger capacitor and discharge resistor thereacross, and

circuit means for connecting said larger capacitor and resistor to said output diagonal pair.